(11-24-2020 )DVT873 Wrote:  What compressor is it? Tangled with an older Holset a while back. Problem ended up being a broken spring. Broke in about 6 places. That design had a sliding plate and reed set up of some type. Spring was supposed to close the plate when it was time to work. It couldn't push it all the way closed...The rebuilds are a real crap shoot today. Doesn't matter whose it is. FWIW most actual compressor problems are in the head regardless of design. That might be why a head is alone is usually half the price of the compressor. Depending on how it sits in the frame changing the whole compressor can be a time eating PIA.

On a slow air build up best way IMO is unhook the discharge line at the compressor and plumb it to shop air. You will hear any leaks much better with the engine off. Remember your gauges don't show you what is happening in the first or "wet" part of the system. You can tee a gauge in if you really want to see. Airdryers cause their own share of problems.

Check the elbow fitting coming out of the compressor. They can carbon up and restrict the flow. Rare but not real rare.

Does the dryer purge or spit off constantly at idle? If it does there is a leak somewhere, usually in the "wet" part of the system, that is not gauged.

Something else I don't like. To save a buck all the OEM's plumb the compressor into the engine air intake system. This means the compressor is trying to get air from the same place as the engine. Usually on the intake side of the turbo. Unless it is fed off the boost side of the turbo, and very few are. Had a talk with a Bendix rep once. Very diplomatic guy. Left me with the impression that Bendix thinks sharing with engine is bad idea.

If I ran a truck two of many things I would do is add a gauge to the wet side and put a stand alone air filter on the compressor. Another thing would be to figure out what I needed to bypass the air dryer. On a nice warm sunny afternoon. Not at 2 am on the side of the road in a snow storm. Figure that out in advance and you'll never need to do it!!

Just my opinions. Worth what they cost most times!